Hi everyone! I think most of us know already about the variation in this preposition:
faoi in Connaght
faoi and fá in Ulster (depending on meaning/context)
fé in Munster.

But from studying Irish dialects (mostly Déise), I found a couple interesting things.

In Déise and Cork Irish, fí is occasionally used as a variant of the much more common fé, such as fé/fí bhrón, fé/fí thuairm, fé/fí dhéin and more. (I don't know if fí also occurs in Kerry and historically other parts of Munster too)

Curiously, I found occurences of fá in Munster and Ossory Irish. In the Déise section of Focail Fholaithe, a collection of words and phrases from South Tipperary (part of the Déise dialect, extremely similar to the Irish of the rest of Waterford), fé, and occasionally fí is what we find, as expected, however the author meantions the use of the phrase so súd agus fá chéile by a speaker from there. There is also the sentence níl bitheamhnach níos mó ná é fá luighe na gréine, where fá luighe appears where in other parts of the same collection we find fé luighe. Also in LASID II, in point 1, which corresponds to An Rinn, we find [fa] dheóidh (fɑ̆ ˈjo:ⁱg').

In the book Labhrann Laighnigh, in the section on Kilkenny, we find the form fé. We also find fé (f'e:) in LASID II for point 6 (Kilkenny), however there is also fa choinne (fə ˈhin'ə), normally found in Ulster only (afaik).

I also found the use of fá in Cork in two different Word Press documents:
The classical form fá is occasionally found, especially in cad fá, why? what for? Doilghís croídhe fá fhearg do chur ar Dhia, heartfelt sorrow at having angered God [PUL1921]
https://corkirish.wordpress.com/wp-content/uploads/2018/11/dictionary.pdf

fé: “under; against”, or faoi in the CO. This preposition was originally fa, but came to be confused with má (“about”), producing fá, which form is occasionally found in PUL’s works. See fá dhéin here, and cad fá?, “why?”, in some of his other works (see Na Cheithre Soisgéil). Fám and fád are also found here, where fém and féd would be expected: these forms are retained in the editing here, as they are not in themselves incorrect.
https://corkirish.wordpress.com/2012/10/24/focloir-do-sheadna/

I also have two questions concerning this preposition.

1. What form was used in the rest of Leinster and the midlands?

2. Are there other instances of fá/fa used in Munster?

Go roibh maith agaibh.

It makes more sense to pick a dialect and learn it than to learn every dialect simultaneously.

I am not learning every dialect simultaneously. I'm learning a specific one, while also interested in other dialects. I don't really understand the intent nor relevance of your comment.

I can't answer any of your questions, but I accidentally found something when I mistyped 'go' while searching on teanglann.

This is what I ended up searching for and it gives fo3, fó = faoi1. So maybe fo and fó were/are forms that were used at some point or in some dialects. I'd assume fo and fó are the same form but the long o might just be getting shortened in much the same way you see with mé, tú etc.

But this is all guesswork on my part!

fo/fu/fa is the historical form of this preposition. It seems it's rarely (if ever) found written with a mark of length in Old Irish sources (see eDIL), but that the mark of length became more common in Middle Irish manuscripts like Lebor na hUidre. That's not to say that it definitely wasn't pronounced with a long vowel, as marks of length are often omitted in Old Irish manuscripts, but the apparent total lack of accent marks in Old Irish sources combined with the variation in spelling (fo/fu/fa) makes me suspect the vowel was probably pronounced something closer to ə originally.

Thank you for your answers.

I'm actually curious to know which modern or historical subdialect would have mainained the form fó, I'm gonna do some research and post an update if I have any luck.

The forms fo and fó can still be found in a number of compound words in Irish (though more than a few of them are neologisms), such as fóchupán ("saucer", or "under cup").

_________________
I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

Oh yeah I've seen some of these too, fotheideal comes to mind.


I have some extra info on this topic that might help.

From The Irish of West Muskerry there's a chapter on the interchange of broad and slender consonants and faoi is given as an example: faoi (fá) > fí and fé. Both fí and fé show up in the texts once a piece (fí bhláth). Although in practice I feel like I've only ever heard fé, at least from Munster speakers on the radio.

The Irish of Ring, Co. Waterford has a similar section giving the transition as faoi > fae > fé. I can't find a mention of fí here though.

Base prepositions were generally unstressed (hence today ag before verbal nouns and ar in some set phrases like ar bith are pronounced as /ə(ɡ), ə(r)/). Old Irish in pretonic position had three short phonemic vowel qualities, typically transcribed /a, o, i/ (hence eg. deuterotonic ·epir changes to prototonic as·beir, both from *exs-beret(i) – there was no pretonic /e/). So fo and fu would be just two ways of writing pretonic /ɸo/. And I suspect the actual vowel was some kind of rounded mid-vowel, like rounded schwa [ə̹], or maybe [ɵ], rather than actual [o] or [u].

fa would be Middle Irish reduction of all short unstressed vowels to schwa, /ɸə/.

The forms faoi, fé of course continue the 3rd person masculine sg. form of the preposition, cf. ag, ar being normally pronounced /eɡ´(ɪ) ~ ɪˈɡ´e, er´/ under influence of the inflected 3rd sg. m. forms aige, air, or go, chuige changing into separate things and new base form chuig appearing in the north (while in Munster chuige getting associated with do-chum, chun).

Also, from random things related to this, worth noting that ó thuaidh ‘northwards’ and ó dheas ‘southwards’ continue OIr. fo·thúaid and fo·dess with this very preposition (and siar, soir, suas, etc. might also have its other form, the preposition being *(s)upo in PIE > *(s)uo > *(s)wo > OIr. fo / *so, with *so perhaps kept as *s- prefixed to vowel-initial words?).